Fungi belonging to genus Geosmithia are widely found throughout nature, and the fungi grow proliferously in agricultural crops such as vegetables and fruits to thereby contaminate foods and drinks made from the agricultural crops. Since fungi belonging to genus Geosmithia form chlamydospores having high heat resistance, the fungi may survive, proliferate, and cause mold growth even after usual sterilization effective against other fungi, such as heat sterilization for acidic drinks. Therefore, there are concerns about the fungi belonging to genus Geosmithia as important harmful fungi causing severe quality accidents. To prevent the accidents by the fungi belonging to genus Geosmithia in foods and drinks and raw materials thereof, it is particularly important to detect and identify the fungi belonging to genus Geosmithia. 
At present, fungi belonging to genus Geosmithia are detected and identified by observing the morphological features of the cultured fungi. In this method, it is necessary to continue the culture until morphological characters appear, and hence, it takes a long period of time (at least 14 days) to achieve the method. Further, the identification of the fungi based on microscopic morphological features requires a high level expertise, and it can not be denied that the identification results may vary depending on judges. Also in some cases, fungi damaged by heating, a chemical agent or the like lose morphogenetic ability, and such fungi cannot form characteristic morphology even after long-term cultivation, thus, the result of the identification is less reliable. Such detection of fungi requiring a long time is not always satisfactory in view of food and drink sanitation, keeping of raw material freshness, distributional restrictions, and the like. Therefore, it is required to establish a detection and identification method which solves the problems of rapidness and reliability.
As a rapid and reliable method of detecting fungi, an amplification method which targets a specific nucleotide sequence of a gene (such as the PCR method) is known (see, for example, Patent Literatures 1 to 4). However, a gene region specific to fungi belonging to genus Geosmithia has not been clarified. Therefore, such method has a problem in that it is difficult to detect fungi belonging to genus Geosmithia specifically and rapidly.